This invention relates to fluid mechanical apparatus for separating and sensing vortex shedding fluid signals in a conduit.
Vortex shedding is a natural phenomenon which can occur when a fluid is made to flow past a bluff or nonstreamlined body. A commonly cited example is the flow around a circular cylinder whose axis is perpendicular to the flowstream. In general, the flow does not follow the shape of the cylinder on the downstream side but separates from the cylinder surface and causes eddies to form. Such eddies or vortices grow in size until they become too large to remain attached to the cylinder. They then break away and are shed downstream at a frequency determined by the flowrate. The growth-shed cycle occurs alternately on either side of the cylinder in a periodic fashion, so that the downstream flow pattern is a staggered arrangement of trails of vortices, often referred to as the Karman vortex street. The direct relationship between shedding frequency and flow velocity makes the phenomenon of vortex shedding pertinent to flowmetering. A simple count of vortices shed is all that is required to establish total flow.
In the past, substantial innovative efforts have been devoted to the development of apparatus for conditioning fluid flow and vortex shedding signals to facilitate their detection and accurately indicating flowrate through a conduit. Among the U.S. Patents disclosing such flow conditioning and vortex sensing facilities are: W. G. Bird, U.S. Pat. Nos. 3,116,639 of Jan. 7, 1964; M. Tomota - H. Yamasaki - Y. Kurita 3,564,915 of Feb. 23, 1971; A. E. Rodely 3,572,117 of Mar. 23, 1971; C. L. McMurtrie--A. E. Rodely 3,587,312 of June 28, 1971; and T. J. Fussell, Jr. 3,732,731 of May 15, 1973 and 3,796,095 of Mar. 12, 1974.
Despite the teachings of the prior art, it has remained a problem reliably to sense vortex shedding signals downstream of a bluff body in a conduit and then accurately to portray a wide range of flowrates through the conduit based on the sensed signals. Reliable sensing has customarily been difficult because the vortex shedding streets often wander and commingle over flowrate ranges of interest. As a consequence, flow signal distortion and cancellation occur and the sensed signals are translated into inaccurate portrayals of flowrate through the conduit.
In view of the foregoing, there has been a need in the prior art for a means for militating against impaired vortex shedding flow signals and errors caused by sensing nonsegregated commingled vortex flow signals downstream of a vortex shedding body.